全文获取类型
收费全文 | 4236篇 |
免费 | 297篇 |
国内免费 | 6篇 |
出版年
2023年 | 21篇 |
2022年 | 48篇 |
2021年 | 77篇 |
2020年 | 43篇 |
2019年 | 50篇 |
2018年 | 108篇 |
2017年 | 80篇 |
2016年 | 131篇 |
2015年 | 218篇 |
2014年 | 233篇 |
2013年 | 286篇 |
2012年 | 313篇 |
2011年 | 321篇 |
2010年 | 186篇 |
2009年 | 174篇 |
2008年 | 224篇 |
2007年 | 190篇 |
2006年 | 220篇 |
2005年 | 180篇 |
2004年 | 174篇 |
2003年 | 171篇 |
2002年 | 152篇 |
2001年 | 94篇 |
2000年 | 98篇 |
1999年 | 73篇 |
1998年 | 33篇 |
1997年 | 28篇 |
1996年 | 27篇 |
1995年 | 21篇 |
1994年 | 30篇 |
1993年 | 24篇 |
1992年 | 44篇 |
1991年 | 33篇 |
1990年 | 31篇 |
1989年 | 28篇 |
1988年 | 21篇 |
1987年 | 25篇 |
1986年 | 17篇 |
1985年 | 17篇 |
1984年 | 17篇 |
1983年 | 20篇 |
1979年 | 18篇 |
1977年 | 15篇 |
1975年 | 16篇 |
1974年 | 20篇 |
1973年 | 17篇 |
1972年 | 20篇 |
1970年 | 13篇 |
1969年 | 13篇 |
1967年 | 13篇 |
排序方式: 共有4539条查询结果,搜索用时 15 毫秒
61.
Diuron treatment for weed control greatly increased anthurium root rot caused by Pythium splendens, P. spinosum, P. vexans and Calonectria crotalariac. Diuron in agar medium was inhibitory to the growth of mycelium, formation and germination of sporangia of P. splendens. Sporangia of P. splendens produced in diuron-amended medium did not differ in pathogenecity to anthurium roots from those produced in diuron-free medium. When diuron was applied to kill weeds in the planting medium, the population of P. splendens in it was not decreased during the test. Diuron was inhibitory to a number of micro-organisms in the platiting medium. Exudation of anthursum roots was not increased by diuron treatment. Increase in severity of anthurium root rot by diuron treatment was similar whether the experiments were performed in the presence or absence of planting medium, suggesting that the enhancing effect of diuron on root rot is mainly due to an increase in susceptibility of the host plants. 相似文献
62.
Hongkui Jin Renhui Yang Gilbert A. Keller Anne Ryan Annie Ko David Finkle Todd A. Swanson WeiLi Diane Pennica William I. Wood Nicholas F. Paoni 《Cytokine》1996,8(12):920-926
Cardiotrophin-1 (CT-1) is a recently discovered cytokine that was isolated based on its ability to induce cardiac myocyte hypertrophy in vitro. In this study, the effects of chronic administration of CT-1 to mice (0.5 or 2 μg by intraperitoneal injection, twice a day for 14 days) were determined. A dose-dependent increase in both the heart weight and ventricular weight to body ratios was observed in the treated groups. The body weights of the animals were unaffected. These results indicate that CT-1 can induce cardiac hypertrophy in vivo. CT-1 was not specific for the heart, however. It stimulated the growth of the liver, kidney, and spleen, and caused atrophy of the thymus. CT-1 administration also increased the platelet counts by 70%, with no change in mean platelet volume. Red blood cell counts were increased in the treated animals, and there was a concomitant increase in haemoglobin concentration. Thus, CT-1 has a broad spectrum of biological activities in vivo. This observation is consistent with previous in-vitro findings showing that the mRNA for CT-1 is expressed in several tissues, and that CT-1 can function through binding to the leukaemia inhibitory factor (LIF) receptor and signalling through the gp130 pathway. 相似文献
63.
P. W. J. Taylor J. R. Geijskes H.-L. Ko T. A. Fraser R. J. Henry R. G. Birch 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1995,90(7-8):1169-1173
Random amplified polymorphic DNA (RAPD) analysis using 10-mer oligonucleotide primers efficiently differentiated sugarcane cultivars and proved suitable for detecting gross genetic change such as that which can occur in sugarcane subjected to prolonged tissue culture, for example in protoplast-derived callus. However, RAPD analysis was not sufficiently sensitive to detect smaller genetic changes that occur during sugarcane genetic transformation. The length of DNA scored for polymorphism per primer averaged 13.2 kb, or 0.0001% of the typical sugarcane genome size of 1.2 × 107 kb (2C). RAPD analysis of sugarcane plants regenerated from embryogenic callus revealed very few polymorphisms, indicating that gross genetic change is infrequent during this tissue culture procedure, although epigenetic effects result in transient morphological changes in regenerated plants. More sensitive variations on the RAPD technique may increase the practicality of DNA-based screening of regenerated plant lines to reveal somaclonal variants. 相似文献
64.
Nanduri VB Hanson RL Laporte TL Ko RY Patel RN Szarka LJ 《Biotechnology and bioengineering》1995,48(5):547-550
10-Deacetylabaccatin III (10 DAB), an important precursor for paclitaxel semisynthesis, is enhanced in yew extracts using C10-deacetylase and C13-deacylase enzymes.(4) C10-deacetylase is an intracellular enzyme produced by the fermentation of a soil microorganism, Nocardioides luteus (SC 13912). During the fermentation of Nocardioides luteus, the growth of cells reaches a maximum growth at 28 h. C10-deacetylase enzyme activity starts at 26 h and peaks at 38 h of the fermentation. The cells are recovered by centrifugation. The C10-deacetylase enzyme was purified from the Nocardioides luteus cells. The enzyme was purified 190-fold to near homogeneity. The purified enzyme appeared as a single band on 12.5% SDS-PAGE analysis with a molecular weight of 40,000 daltons. (c) 1995 John Wiley & Sons, Inc. 相似文献
65.
66.
67.
Acetylcholinesterase (AChE) purified from mouse brain was reconstituted in liposomes of a different charge, and the properties of liposome-associated AChE were investigated. Relative to the Km value (38.5 M) of AChE bound to a neutral liposome, the value of AChE reconstituted in a negatively-charged liposome decreased to 23.3 M, whereas that of AChE in a positively-charged liposome increased to 90.9 M. Additionally, AChE bound to a positively-charged liposome expressed a wider range of optimum pH than the enzyme in a negatively-charged liposome. In a stability study, it was found that soluble AChE was unstable at pH 5.5 and 7.4, while it was relatively stable at pH 10. Noteworthy, the immobilization of AChE to liposome enhanced the stability of soluble enzyme at acidic and neutral pH. Moreover, in the stabilization of the enzyme, a neutral liposome was more effective than charged liposomes, of which a positively-charged liposome was more effective than a negatively-charged liposome at acidic pH. Based on these results, it is proposed that while the Km value and the pH dependence of AChE activity are affected by the charge of liposome, the stability of AChE is determined mainly by a hydrophobic binding to a phospholipid membrane.This work was supported in part by Agency for Defense Development. 相似文献
68.
69.
The presence of actin in nuclei: a critical appraisal. 总被引:5,自引:0,他引:5
To assess the significance of actin associations with nuclei, we have examined Amoeba proteus nuclei for the presence of labeled actin under a variety of circumstances without (in most instances) isolating nuclei or breaking up cytoplasms prior to the extraction of proteins.We first established that: the 42,000 dalton proteins (presumed to be actin) present in cytoplasm and non-isolated nuclei are identical electrophoretically; the putative actin of amebas has the same size and almost the same isoelectric point as rat muscle actin; and the peptide “fingerprints” of putative ameba actin and rat actin are very similar after tryptic digestion. We therefore concluded that the 42,000 dalton protein of ameba is actin.We determined that: the concentrations of actin in the cytoplasm and nucleus of amebas are the same; actin is readily lost from nuclei that are released from lysed cells; shortly after a 35S-labeled nucleus is transplanted into unlabeled cytoplasm, or an unlabeled nucleus is transplanted into 35S-labeled cytoplasm, the concentration of 35S-actin in nucleus and cytoplasm is the same; and when cells containing 35S-actin are subjected to long chase periods on unlabeled food, the concentrations of 35S-actin in nucleus and cytoplasm fall in parallel. These observations taken together suggest that actin is not tightly associated with nuclei. Rather, actin may associate with nuclei for the trivial reason that the nuclear envelope is no barrier to free movement of that protein between the two compartments.We conclude that the mere presence of actin in nuclei is insufficient grounds for assuming that it has any role in nuclear functions, such as, for example, chromosome condensation. 相似文献
70.